Fabrication of a reinforcement structure for a tire with volumetric control

ABSTRACT

Apparatus for fabricating a reinforcement structure for a tire, the said reinforcement structure comprising threads disposed substantially parallel to each other, the said apparatus being intended to be used in cooperation with a substantially toroidal form ( 1 ) on which the said reinforcement structure is progressively constructed by depositing arches of the said thread side by side along a desired trajectory for the said thread on the surface of the said form, the said apparatus comprising an assembler ( 5 ) comprising an entry for receiving the threads ( 2 ), a rubber-coating chamber ( 50 ), a volumetric pump for delivering a rubber composition inside the rubber-coating chamber, an outlet orifice for a strip ( 20 ) comprising the threads joined by the said composition, a device ( 4 ) for depositing the said strip comprising a reference framework with respect to which it is possible to install the said form at a known position.

FIELD OF THE INVENTION

The present invention concerns the manufacture of tires. More precisely,it relates to the laying of threads in order to constitute areinforcement structure for a tire. More particularly, it proposes meansable to fabricate such a reinforcement structure on a form close to oridentical to the shape of the internal cavity of the tire, that is tosay a substantially toroidal form, supporting the blank of a tire duringits manufacture.

BACKGROUND OF THE INVENTION

In this technical field, methods and apparatuses are already known whichmake it possible to integrate the fabrication of tire reinforcementstructures in the assembly of the tire itself. This means that, ratherthan using semi finished products, such as reinforcement plies, one ormore reinforcement structures are produced in situ, at the time ofmanufacture of the tire, and using a single coil of thread.

Amongst these methods and apparatuses, the solution described in thepatent U.S. 4,804,436 proposes to produce reinforcement structures froma single thread. This solution in particular allows the production of areinforcement structure under the tread.

It is also well known how to produce a reinforcement structure for atire from a strip comprising reinforcement threads parallel to eachother and embedded in an elastomeric composition such as a rubbercomposition. Such a strip is cut into portions and the portions aredeposited adjacent to each other on a fabrication support, where thearchitecture so requires, in order to produce the tire reinforcementstructure desired by the tire designer. Amongst the various variants ofa method of fabrication from strips, the patent U.S. Pat. No. 1,728,957can be cited, which describes fabricating strips and then cuttingportions and arranging strips on a substantially toroidal fabricationform, ensuring that a pitch which is as constant as possible is keptbetween the adjacent threads in the portion.

The technique of fabricating reinforcement structures from a strip hashowever not found many industrial applications since on the one hand itdoes not have the productivity of fabrication from plies and on theother hand it does not have the flexibility and precision of a techniqueof fabrication from an individual thread. When it is wished to fabricatea tire according to a technique affording little or absolutely noconformation of the uncured product during its manufacture, it is ofprime importance to be able to deposit the reinforcement structures andthe uncured rubber products constituting the future tire with very greatprecision with regard to both their positioning and the quantity ofmaterial deposited on the fabrication form.

SUMMARY OF THE INVENTION

The objective of the present invention is to propose a method andequipment which allow the fabrication of a reinforcement structure for atire by depositing on a fabrication form, and this with very greatprecision in laying, a high level of efficiency, and by using meanswhich are as simple as possible, guarantees of very great industrialrobustness. Advantageously, this fabrication form is close to the shapeof the internal cavity of the future tire.

The invention proposes a method of manufacturing a tire comprising areinforcement structure comprising threads disposed substantiallyparallel to each other, the method using a substantially toroidal formon which the said reinforcement structure is progressively constructed,the method comprising the following steps:

-   -   forming a group of several threads disposed substantially        parallel to each other,    -   joining the threads by means of an elastomeric composition in        order to form a strip,    -   depositing the said strip along a predetermined trajectory on        the surface of the said form, wherein, for a unit length of        strip, a unit quantity of the said composition is used,        determined according to the share taken by the said unit length        of strip after its deposition on the form during the manufacture        of the tire.

The invention also proposes an apparatus for the in situ fabrication ofa strip for fabricating a reinforcement structure for a tire anddepositing the strip on a form, with volumetric control. This apparatusfor fabricating a reinforcement structure for a tire, the saidreinforcement structure comprising threads disposed substantiallyparallel to each other, the said apparatus being intended to be used incooperation with a substantially toroidal form on which the saidreinforcement structure is progressively constructed by depositingarches of the said thread side by side along a desired trajectory forthe said thread on the surface of the said form, comprises:

-   -   an assembler comprising an entry for receiving the threads, a        rubber coating chamber, a volumetric pump for delivering an        elastomeric composition inside the chamber, and an exit orifice        for a strip comprising the threads joined by the said        composition,    -   a device for depositing the said strip comprising a reference        framework with respect to which the said form can be installed        at a known position, the depositing device comprising a head        equipped with a guidance passage for the strip and a        rolling-down member intended to cooperate with the said form,        the apparatus comprising at least one actuator for guiding the        said head with respect to the reference framework.

In a particular embodiment, the apparatus enables the strip to bedeposited on the said form, with turning over from one layer to thenext.

It should be noted first of all that, in the context of the presentdocument, the term “thread” must of course be understood in an entirelygeneral sense, encompassing a single filament, a multifilament, anassembly such as for example a cable or a yarn, or a small number ofcables or yarns grouped together, whatever the nature of the material,and that the thread is precoated with an elastomer such as rubber ornot. The term “strip” is used for designating an assembly of severalparallel threads, connected by a matrix of uncured rubber. The term“portion” is used to designate a piece of strip, created by cutting acertain length of strip. A portion of strip allows the deposition ofseveral arches of thread. “Arch” means a limited length of thread,stretching from a singular point to another in the tire as a finishedvulcanized product. “Trajectory” means the exact trajectory of an archin the finished tire. A set of arches deposited over the entireperiphery of the tire forms a reinforcement structure. An arch, in themeaning defined here, can form part of a casing or of a crownreinforcement or any other type of reinforcement structure.

Fundamentally, the invention relates to the depositing of successiveportions of thread strip, in a configuration that is as close aspossible to the configuration of the final product. It is of littleimportance if the reinforcement structure is, in order to be complete,fabricated in several successive rotations of the form or not, norwhether the portions successively deposited are deposited adjacent or onthe contrary with a certain amount of space between them. The depositingof portions of strip on the fabrication form is carried out according tothe trajectory sought. In the case (particular and non-limiting) of aform whose external surface defines the internal surface of the tire,delimiting the internal cavity of the tire, the deposition trajectory ofa portion of strip is merged with the trajectory of an arch of thread inthe tire.

When positions, orientations or directions are defined with the words“radially, axially, circumferentially”, or when radii are spoken of, theform on which the tire is fabricated, or the tire by itself, is taken asa reference. The reference geometric axis is the axis of rotation of theform.

According to a particular aspect of the method proposed by theinvention, the unit quantity is obtained by means of a volumetriccontrol, the share taken being estimated according to the volumeoccupied by the said unit length. An extruder of a volumetric nature istherefore preferably used. In a variant, it would be possible to controlthe weights and to aim at contributions by weight. A control unitprovides the synchronized control of the unit quantity of compositionused and of the deposition of the unit length of the strip on the form.Advantageously, the strip is formed by members disposed at a fixedposition in space, and the strip is then brought to a laying head, atleast one laying outlet of which is able to move with respect to theform. Thus the movable members are less heavy; it is therefore easier tomove them. Naturally, preferably, the said unit quantity is controlledby taking account of the length of strip accumulated between theformation of the strip and the laying head.

According to another particular aspect of the method proposed by theinvention, the progressive construction of the reinforcement structurethen takes place whilst the said form is in continuous rotation, bymoving the laying head in a plane comprising the axis of rotation of theform. In order to obtain all the relative movements required for thelaying of the strip on the surface of the form, it is possible to movethe laying outlet transversely and parallel with respect to the axis ofthe form and to make the form rotate about its axis, these movementsbeing judiciously combined. It is possible to design an implementationof the control where the control of the unit quantity of composition iscontrolled by the relative movement between the laying outlet and theform, or vice-versa. The control of the unit quantity is advantageouslycontrolled by the rotation of the form. A strip with a constantcross-section is preferably formed, wherein the said volume occupied bythe unit length is determined according to the radius of deposition onthe surface of the form and the angle of the arc occupied by the unitlength on the surface of the form.

According to a particular and non-limiting characteristic of the methodproposed by the invention, in order to join the threads by means of anelastomeric composition, the said threads are introduced in parallelinto an assembler comprising a formation chamber inside which the saidcomposition is delivered, the assembler comprising an outlet orifice forthe strip.

BRIEF DESCRIPTION OF THE DRAWINGS

The remainder of the description gives a clear understanding of all theaspects of the invention, relying on the following figures, which show aparticular and non-limiting example of an apparatus according to theinvention:

FIG. 1 depicts in perspective an apparatus according to the invention.

FIG. 2 is a view in the direction of the arrow B in FIG. 1.

FIG. 3 is an enlargement showing in more detail the member referred toby reference 5 in FIG. 1.

FIG. 4 is a view in perspective of the same apparatus as the oneillustrated by FIG. 1 in another operating phase.

FIG. 5 is a view in the direction of the arrow C in FIG. 4.

FIG. 6 is an enlargement showing in more detail the member referred toby reference 41 in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a form 1 can be seen on which there are deposited,successively and in the order required by the architecture of the tire,all the elements making up the latter. This form 1, which issubstantially rigid, can for example be a rigid metallic core in severalpieces, a description of which can be found in patent application EP1075928.

The reinforcement thread 2 used is stored upstream of the installation,for example on a set of reels, each mounted on a spindle forming part ofa rack for storing as many reels of thread as there are threads in astrip. A pay-off device (not shown in order not to overload the drawing)for the threads 2 makes it possible to set in motion the threads 2 so asto bring them to the apparatus for fabricating a reinforcement structurefor a tire. The pay-off device for the threads 2 preferably comprises asmany motors as there are reels, each motor allowing to set in motion onethread 2. The pay-off device for the threads 2 makes it possible to setin motion the threads 2 with a well-controlled tension, for example aslow as possible.

The apparatus proper comprises essentially an assembler 5 and a layinghead 4. The assembler 5 comprises an entry orifice 51 (see FIG. 3) asfar as which the threads 2 travel individually (FIGS. 1, 3 and 4 areschematic). The assembler 5 comprises a feed orifice 53 for introducinga ribbon 30 of an uncured rubber composition adapted to the use of thestrip in the future tire. There can also be seen a reel 3 on which thesaid ribbon 30 is wound. The ribbon 30 is inserted in the feed orifice53 of the assembler 5. The assembler 5 comprises a delivery device of avolumetric character, namely a volumetric pump 54.

According to one characteristic of the present invention, the quantityof rubber composition for fabricating the strip is controlled positivelyaccording to the position of the strip on the form. In the embodimentdescribed here, this is done using a mechanically volumetric pump. Thevolumetric pump 54 is for example a gear pump, as shown, or a pistonpump. A description of a piston pump can be found in the patent U.S.Pat. No. 5,655,891.

The delivery device (also referred to as a “volumetric pump 54”) allowsto deliver uncured rubber 30 into a chamber 50 for forming a strip 20.The assembler 5 comprises an outlet orifice 52 for the strip 20. Theassembler 5 comprises two rollers 56 around which the strip 20 is wound.At least one of the rollers 56 is set in rotation by a motor 57.

The laying head 4 is mounted opposite the form 1. It comprises aframework 40 on which a cradle 41 is mounted by means of the mechanismdescribed below. The cradle 41 is mounted on a carriage 43 by means of apivot 42. By virtue of the pivot 42, the cradle 41 can be oriented at anangle α visible in FIG. 6. The laying head 4 also comprises arolling-down device 49 comprising at least one roller 47 (two similarrollers for a better grip on the strip). The rolling-down device 49 cantilt about the axis YY by an angle δ. The rolling-down device 49 allowsto apply the strip 20 with a certain pressure on the form 1. Thecarriage 43 is mounted on a guideway 44 substantially parallel to theaxis of rotation XX of the form 1. The guideway 44 is itself mounted ontwo rails 46 parallel to each other, substantially perpendicular to thesaid guideway 44, by means of two slides 45.

In the cradle 41, a frame 6 is mounted on two bearings 60. Each of thebearings 60 comprises a slot 61 centered on the axis of the bearings 60.The strip 20 can travel through the slots 61, which provide a guidancepassage for the strip 20. The frame 6 can rotate through at least 180°with respect to the cradle 41. The frame 6 thus mounted on the cradle 41forms a turning-over mechanism and is a particular and non-limitingembodiment of a device for depositing the said strip comprising amechanism for turning over the strip making it possible to invert theface of the strip which is brought in contact with the form by thelaying head.

A member 48 for cutting the strip, such as a guillotine (the blade ofwhich can be seen in FIG. 6, the counter-blade being omitted), isintegrated in the frame 6, and therefore in the laying head 4.

The form 1 is supported by a hub carrier 10, comprising a hub to whichthe form 1 is attached, and comprising the necessary motorizationallowing to set in motion the form 1, with azimuth α controlled at alltimes. The framework 40 is mounted so as to be fixed with respect to thehub carrier 10, at least during the functioning of the installation (theaspects of approach and removal of the form 1 will not be dealt withhere).

The cradle 41 can be presented in all required positions with respect tothe form 1 (see FIGS. 1, 2, 4 and 5). That is to say it can be movedradially with respect to the form 1 (arrow F₂), can slide transverselywith respect to the form 1 (arrow F₁), and can be inclined around theaxis YY (angle δ) with respect to the form 1, and oriented at the angleφ. It is therefore possible to present the strip 20 to the form 1 in allpositions required in order to ensure, in combination with the rotationof the form 1, its deposition according to any required depositiontrajectory. Thus it is possible to deposit the strip 20 at any angle βwith respect to the meridian plane CP in order to form a reinforcementstructure at any angle β, even variable.

The functioning of the apparatus according to the invention will now bedescribed.

According to a particular aspect of the invention, the apparatuscomprises a unit for controlling the rotation movement of the form andthe movement of the head with respect to the frame and the volumetricpump, the said unit being configured so that the quantity , per unitlength of strip, of composition inserted inside the coating chamber bythe volumetric pump is a function of the position occupied by the unitlength of strip during its deposition on the form.

According to another particular aspect of the invention, the apparatuscan comprise a unit controlling the rotation movement of the form andthe movement of the head with respect to the framework and thevolumetric pump, the said unit being configured so that the volume, perunit length of strip, of composition inserted inside the coating chamberby the volumetric pump is a function of the volume occupied by the saidunit of length of the strip after its deposition on the form.

It can be seen in FIG. 1 that the laying head 41 is close to theright-hand shoulder of the future tire, whose shape can be clearlyimagined by examining the rigid core 1 on which it will be constructed.The free end of the strip, previously cut forming an angle β, ispresented to the surface of the form and is held there by the roller 47,at the required point in the shoulder area of the future tire. Naturallythe material against which the strip 20 is applied must be such that thestrip 20 has a tendency to remain bonded. Typically the form is alreadycoated with uncured rubber, naturally sticking to the uncured rubbercomposition 30.

The elastomeric composition is delivered into the formation chamber 50by means of the delivery device 54. The latter makes it possible tointroduce the uncured rubber at a certain pressure inside the formationchamber 50, so that the rubber fills it completely. Whilst all thethreads 2 pass through the formation chamber 50, a controlled volume ofrubber is introduced into the formation chamber 50. The basic parameterfor the control provided by the control unit is the rotation of the form1. Moreover, the means of moving the laying head 4 with respect to theform 1, whose functioning is described below, are themselves controlledso as to produce a certain deposition trajectory according to thearchitecture of the tire to be manufactured. The radius at which thestrip is deposited is therefore in particular known at all times, whichmakes it possible, given the constitution of the strip, which is alsodetermined by the architecture of the tire, to calculate the volumedeposited on the form. The volume occupied by the reinforcement threadsin themselves is also known.

It is from the rotation of the form 1, and considering its knowngeometry and the movements of the laying head 41, and considering thestock in hand (the stock of strip existing between the formation chamber50 and the point where the strip joins the form 1), that the controlunit therefore determines the volume of rubber to be introduced into theformation chamber 50. At the same time, the threads 2 set in motion thissame volume of rubber out of the formation chamber 50. Thus the strip 20appearing at the extrusion orifice 52 comprises all the threads 2unwound in parallel and a well-controlled quantity of impregnationrubber 30. The strip 20 is itself motorized by means of rollers 56 andthe motor 57 so that it is set in motion out of the chamber 50 with asubstantially constant tension.

A compensation area can be seen, interposed between the assembler 5 andthe laying device 4, in which a certain (known) length of strip isaccumulated. This makes it possible to ensure without impact theessentially continuous functioning of the assembler 5 and theessentially discontinuous functioning of the laying head 41, andtherefore allows to smoothen the formation of the strip with respect tothe variations in speed of the form 1, with regard to which it wasstated above that it was a basic parameter of the control provided bythe control unit.

So as to be able to avoid the deleterious effects of drift infunctioning, it is advantageous to measure the length of strip actuallyused, independently of the control parameters which continuouslycalculate the length of strip to be manufactured. A measuring roller,preferably independent of the roller or rollers 47 (not shown), isequipped with a coder which makes it possible to know at any moment andwith precision the length of strip deposited on the form 1. This makesit possible to adjust the manufacture of the strip to the quantity ofstrip actually deposited on the form 1.

The core 1 is set in rotation (angle α) and the cradle 41 is able tomove with respect to the form. The cradle 41 is moved in translationfrom right to left (arrow F₁) in order to regain the position in whichit is drawn in broken lines, all this synchronously. Whilst the cradle41 moves over a width which corresponds to the width of thereinforcement structure fabricated under the tire tread, the core 1 isdriven in rotation so as to travel over an arc α. During thesemovements, the strip 20 is applied against the form 1 by therolling-down roller 47. Towards the end of these movements, theguillotine integrated in the laying head cuts the strip whilst complyingwith the angle which it is wished to give to the edge of the strip. Thisangle corresponds to the angle which must be formed by the edge of thefollowing portion. There is therefore no waste of material between twosuccessive portions.

To allow automatic functioning, the strip is continuously in engagementin the laying head 4. An automatic advance device (not shown) for thestrip after cutting makes it possible for its free end to be once againin engagement with the rolling-down device 49 after cutting, so as to beable to be once again presented to the form 1 and pressed against it.The control unit continuously knows the length of the accumulated andnon-positioned strip, which makes it possible to take account of thisstock in hand in the volumetric control of the unitary quantity ofcomposition per unit length of strip.

Step by step, the required number of portions of strip are deposited onthe form, for example adjacent to each other, progressively covering theentire periphery of the fabrication form. Through the formation of thestrip as described here, the pitch between all the threads is constantin the strip. In the end, it is possible to arrange so as to keep thesame pitch or a different pitch between the adjacent threads issuingfrom two different strips.

The operation of depositing the portions of strip 20 may give rise to asmany complete turns of the form 1 as there are portions of strip inorder to produce a complete reinforcement structure or, as soon as thelaying head joins the left-hand shoulder of the future tire, it may bereturned to the opposite shoulder without interrupting the rotation ofthe form 1 and another portion of strip can be deposited as soon as thelaying head rejoins the right-hand shoulder. It suffices to arrange toleave a space between the two positioned portions corresponding to aninteger number of portions which will be installed during successiverotations.

In order to pass from one layer to the following layer (or in otherwords to pass from one ply to the following ply), according to aparticular but advantageous characteristic of the present invention, aturning-over device is integrated in the laying head. It suffices tomake the frame 6 pivot through 180° and the strip 20 is ready to effectthe deposition of the following layer. The movements disclosed above arethen repeated, except that the action is from left to right instead ofworking from right to left. This is what is depicted in FIG. 4.

In a particular application, the invention makes it possible tofabricate a reinforcement structure comprising many arches of threadsobtained by successively depositing adjacent portions of strip createdby cutting the strip. In a more particular case still, the saidreinforcement structure forms part of a belt situated underneath thetread. In another more particular case, the said reinforcement structureforms part of a carcass going at least as far as a bead.

The invention allows depositing the reinforcement threads in groupsforming a strip with a laying precision much better than what wasproposed by the state of the art up to the present time for techniquesof fabricating from strips. Moreover, by virtue of the stripturning-over device proposed by the present invention, the passage fromone layer to another with change of angle formed by the reinforcementthreads can take place extremely quickly, without in any way slowingdown the rate of manufacture of an apparatus according to the invention,and without waste of material.

1. Method of manufacturing a tire comprising a reinforcement structurecomprising threads disposed substantially parallel to each other, themethod using a substantially toroidal form on which the saidreinforcement structure is progressively constructed, the methodcomprising the following steps: forming a group of several threadsdisposed substantially parallel to each other, joining the threads bymeans of an elastomeric composition in order to form a strip, depositingthe said strip along a predetermined trajectory on the surface of thesaid form, wherein, in order to form a unit length of strip, a unitquantity of the said composition is used, determined according to theshare taken by the said unit length of strip after its deposition on theform during the manufacture of the tire.
 2. Method according to claim 1,in which the unit quantity used is obtained by means of a volumetriccontrol, the share taken being estimated according to the volumeoccupied by the said unit length.
 3. Method according to claim 1,wherein a strip with a constant cross-section is formed, and wherein thesaid volume occupied by the unit length is determined according to theradius of deposition on the surface of the form and the angle of the arcoccupied by the unit length on the surface of the form.
 4. Methodaccording to claim 1, wherein the strip is formed by members disposed ata fixed position in space, and in which the strip is then brought to alaying head, at least one laying outlet of which is able to move withrespect to the form, and in which the said unit quantity is controlledby taking account of the length of the strip accumulated between theformation of the strip and the laying head.
 5. Method according to claim4, wherein the progressive construction of the reinforcement structuretakes place whilst the said form is in rotation, by moving the layinghead in a plane comprising the axis of rotation of the form, the controlof the unit quantity being controlled by the rotation of the form. 6.Method according to claim 1, wherein, in order to join the threads bymeans of an elastomeric composition, the said threads are introduced inparallel into an assembler comprising a formation chamber inside whichthe said composition is delivered, the assembler comprising an outletorifice for the strip.
 7. Method according to claim 1, wherein the saidreinforcement structure comprises many arches of threads obtained bysuccessively depositing adjacent portions of strip created by cuttingthe strip.
 8. Method according to claim 1, wherein the saidreinforcement structure forms part of a belt situated underneath thetread.
 9. Method according to claim 1, wherein the said reinforcementstructure forms part of a carcass.
 10. Apparatus for fabricating areinforcement structure for a tire, the said reinforcement structurecomprising threads disposed substantially parallel to each other, thesaid apparatus being intended to be used in cooperation with asubstantially toroidal form on which the said reinforcement structure isprogressively constructed by depositing arches of the said thread sideby side along a desired trajectory for the said thread on the surface ofthe said form, the said apparatus comprising: an assembler comprising anentry for receiving the threads, a rubber coating chamber, a volumetricpump for delivering an elastomeric composition inside the chamber, anexit orifice for a strip comprising the threads joined by the saidcomposition, a device for depositing the said strip comprising areference framework with respect to which the said form can be installedat a known position, the depositing device comprising a head equippedwith a guidance passage for the strip and a rolling-down member intendedto cooperate with the said form, the apparatus comprising at least oneactuator for guiding the said head with respect to the referenceframework.
 11. Apparatus according to claim 10, comprising a unit forcontrolling the rotation movement of the form and the movement of thehead with respect to the framework and the volumetric pump, the saidunit being configured so that the quantity, per unit length of strip, ofcomposition inserted inside the chamber by the volumetric pump is afunction of the position occupied by the said unit length of stripduring its deposition on the form.
 12. Apparatus according to claim 10,comprising a unit for controlling the rotation movement of the form andthe movement of the head with respect to the framework and thevolumetric pump, the said unit being configured so that the volume, perunit length of strip, of composition inserted inside the chamber by thevolumetric pump is a function of the volume occupied by the said unitlength of strip after its deposition on the form.
 13. Apparatusaccording to claim 10, comprising a strip length compensation area,disposed between the assembler and the depositing device.
 14. Apparatusaccording to claim 10, wherein the device for depositing the said stripcomprises a member for cutting the strip.
 15. Apparatus according toclaim 13, wherein the device for depositing the said strip comprises amechanism for turning over the strip making it possible to invert theface of the strip which is brought in contact with the form by thelaying head.